Electrochemical cell including a plasma source and method of operating the electrochemical cell

Abstract

An electrochemical cell includes a container at atmospheric pressure comprising a liquid electrolyte and a first electrode at least partially immersed in the electrolyte. A plasma source is spaced apart from a surface of the electrolyte by a predetermined spacing, and a plasma spans the predetermined spacing to contact the surface of the electrolyte. A method of operating the electrochemical cell entails providing a first electrode at least partially immersed in a liquid electrolyte and producing a plasma in contact with a surface of the electrolyte at atmospheric pressure. The plasma acts as a second electrode, and a current is generated through the electrolyte. Electrochemical reactions involving at least the second electrode are initiated in the electrolyte.

The invention claimed is: 
     
       1. An electrochemical cell having a closed circuit configuration comprising:
 an open container at atmospheric pressure comprising a liquid electrolyte; 
 a first electrode at least partially immersed in the liquid electrolyte; 
 a plasma source spaced apart from a surface of the liquid electrolyte by a predetermined spacing; and 
 a plasma spanning the predetermined spacing to contact the surface of the liquid electrolyte, 
 wherein the plasma source comprises a hollow conductive body including a first opening and a second opening and a cavity therebetween, the first opening comprising a gas inlet to the cavity and the second opening being separated from the surface of the liquid electrolyte by the predetermined spacing. 
 
     
     
       2. The electrochemical cell of  claim 1 , wherein the first electrode is fully immersed in the liquid electrolyte. 
     
     
       3. The electrochemical cell of  claim 1 , wherein the liquid electrolyte comprises an aqueous solution. 
     
     
       4. The electrochemical cell of  claim 1 , wherein the liquid electrolyte comprises at least one of an acid, a metal salt, and a stabilizer. 
     
     
       5. The electrochemical cell of  claim 4 , wherein the first electrode comprises a metal selected from the group consisting of Ag, Al, Au, Fe, Pt, and Cu, and wherein the acid is an etchant of the metal. 
     
     
       6. The electrochemical cell of  claim 1 , wherein the plasma serves as a second electrode. 
     
     
       7. The electrochemical cell of  claim 1 , wherein the plasma source is electrically connected to a power supply and the first electrode is electrically connected to ground. 
     
     
       8. The electrochemical cell of  claim 1 , wherein the predetermined spacing is between about 0.5 mm and about 5 mm. 
     
     
       9. The electrochemical cell of  claim 1 , wherein the hollow conductive body is a conductive tube. 
     
     
       10. The electrochemical cell of  claim 9 , wherein the cavity of the conductive tube comprises a diameter of about 200 microns or less. 
     
     
       11. A method of operating an electrochemical cell, the method comprising:
 providing a first electrode at least partially immersed in a liquid electrolyte comprising an aqueous solution; 
 producing a plasma in contact with a surface of the liquid electrolyte at atmospheric pressure to generate a current through the liquid electrolyte, the plasma acting as a second electrode; 
 initiating electrochemical reactions in the liquid electrolyte involving at least the second electrode, 
 wherein producing the plasma comprises: flowing a gas through a hollow conductive body including a first opening and a second opening and a cavity therebetween, the first opening comprising a gas inlet to the cavity and the second opening being separated from the surface of the liquid electrolyte by a predetermined spacing; and applying a voltage across the hollow conductive body and the first electrode. 
 
     
     
       12. The method of  claim 11 , wherein the electrochemical reactions include reduction of metal ions in the liquid electrolyte by free electrons from the plasma. 
     
     
       13. The method of  claim 12 , wherein the electrochemical reactions include anodic dissolution of the first electrode to produce the metal ions in the liquid electrolyte. 
     
     
       14. The method of  claim 12 , wherein the liquid electrolyte includes a metal salt, the metal salt providing the metal ions. 
     
     
       15. The method of  claim 11 , wherein the current generated through the liquid electrolyte is between about 1 mA and 10 mA. 
     
     
       16. The method of  claim 11 , wherein the predetermined spacing is between about 0.5 mm and about 5 mm. 
     
     
       17. A method of producing metal nanoparticles, the method comprising:
 providing a first electrode at least partially immersed in a liquid electrolyte at ambient temperature, the liquid electrolyte including an analyte molecule; 
 producing a plasma in contact with a surface of the liquid electrolyte at atmospheric pressure to generate a current through the liquid electrolyte, the plasma acting as a second electrode; 
 reducing metal ions in the liquid electrolyte by free electrons from the plasma to form metal nanoparticles in the liquid electrolyte. 
 
     
     
       18. The method of  claim 17 , wherein the metal ions in the liquid electrolyte are generated by anodic dissolution of the first electrode. 
     
     
       19. The method of  claim 17 , wherein the liquid electrolyte includes a metal salt, the metal salt providing the metal ions. 
     
     
       20. The method of  claim 17 , wherein the analyte molecule is present in the liquid electrolyte at a concentration of from about 10 −10  M to about 10 −5  M. 
     
     
       21. The method of  claim 17 , wherein the analyte molecule is a Raman-active molecule. 
     
     
       22. The method of  claim 17 , further comprising detecting a signal from the analyte molecule. 
     
     
       23. The method of  claim 22 , wherein the signal is a Raman scattering signal. 
     
     
       24. The method of  claim 22 , wherein the signal is detected as the plasma is produced. 
     
     
       25. The method of  claim 17 , wherein the plasma is produced for a time duration of at least about 5 minutes, a concentration of the metal nanoparticles in the liquid electrolyte increasing during the time duration. 
     
     
       26. The method of  claim 25 , wherein the time duration is at least about 15 minutes.